Normal pregnancy requires extensive changes in the maternal cardiovascular system. A new vascular bed (the uteroplacental unit) requires up to 25% of maternal cardiac output. To accommodate this increase in uterine blood flow, the uterine vasculature appears to be fully dilated. Maternal stress (e.g., fright, drug abuse) can markedly reduce uterine blood flow. This decreased uterine blood flow must be due to increased tone in the larger uterine arteries because the myometrial resistance vessels lose the smooth muscle in pregnancy. Lack of dilation of the uterine arteries can result in in utero death or fetal growth retardation with consequent birth defects. Furthermore, considerable evidence exists that utero-placental perfusion insufficiency can be a causative factor in the development of pregnancy-induced hypertension. The objective of this application is to test the hypothesis that mechanisms for pregnancy-induced vasodilation of human uterine arteries involve increased release of nitric oxide (NO) and calcitonin gene-related peptide (CORP), and attenuated adrenergic and enhanced nonadrenergic-noncholinergic (NANC) neurotransmissions. The proposed research will focus on cellular or molecular mechanisms of pregnancy-induced functional changes in endothelium, nerves and smooth muscle of isolated human uterine arteries. There are 4 specific aims: l) The effect of pregnancy on NO synthesis, release and effects will be determined. NO synthase (NOS) activity will be measured by the arginine to citrulline conversion method. The inducible isoform of NOS (iNOS) will be differentiated from the constitutive NOS (cNOS) by localization, calcium- dependency, sensitivity to NOS inhibitors and by Western and Northern blot analyses. The contribution of pregnancy-induced increase in NO in regulating vascular tone will be assessed by the use of inhibitors of NO synthesis, effects and inactivation in the uterine artery bioassays. 2) The vasodilatory role of CGRP during pregnancy will be determined. Spontaneous, agonist- and nerve-induced release of CGRP will be measured directly by radioimmunoassays and indirectly by the use of capsaicin and CGRP antagonists. 3) The role of NO in pregnancy-induced depletion of norepinephrine will be examined by studying the effect of NO-donors on adrenergic innervation using bioassays, HPLC, and immunocytochemical techniques. 4) The relative contribution of NO and CGRP in NANC neurotransmission will be assessed. The results of the proposed research should provide new knowledge about the physiological regulation of uterine blood flow during pregnancy. Such knowledge will contribute to the development of methods and drugs for the prevention and treatment of uteroplacental perfusion insufficiency and, thus, avert the complications (e.g., fetal death, birth defects, maternal hypertension) attributable to inadequate utero-placental perfusion.